function PCMPlayer (option) {
  this.init(option)
}

PCMPlayer.prototype.init = function (option) {
  var defaults = {
    encoding: '16bitInt',
    channels: 1,
    sampleRate: 8000,
    flushingTime: 1000
  }
  this.option = Object.assign({}, defaults, option)
  this.samples = new Float32Array()
  this.flush = this.flush.bind(this)
  this.interval = setInterval(this.flush, this.option.flushingTime)
  this.maxValue = this.getMaxValue()
  this.typedArray = this.getTypedArray()
  this.createContext()
}

PCMPlayer.prototype.getMaxValue = function () {
  var encodings = {
    '8bitInt': 128,
    '16bitInt': 32768,
    '32bitInt': 2147483648,
    '32bitFloat': 1
  }

  return encodings[this.option.encoding] ? encodings[this.option.encoding] : encodings['16bitInt']
}

PCMPlayer.prototype.getTypedArray = function () {
  var typedArrays = {
    '8bitInt': Int8Array,
    '16bitInt': Int16Array,
    '32bitInt': Int32Array,
    '32bitFloat': Float32Array
  }

  return typedArrays[this.option.encoding] ? typedArrays[this.option.encoding] : typedArrays['16bitInt']
}

PCMPlayer.prototype.createContext = function () {
  this.audioCtx = new (window.AudioContext || window.webkitAudioContext)()

  // context needs to be resumed on iOS and Safari (or it will stay in "suspended" state)
  this.audioCtx.resume()
  this.audioCtx.onstatechange = () => {
    // console.log(this.audioCtx.state)
  }   // if you want to see "Running" state in console and be happy about it

  this.gainNode = this.audioCtx.createGain()
  this.gainNode.gain.value = 1
  this.gainNode.connect(this.audioCtx.destination)
  this.startTime = this.audioCtx.currentTime
}

PCMPlayer.prototype.isTypedArray = function (data) {
  return (data.byteLength && data.buffer && data.buffer.constructor == ArrayBuffer)
}

PCMPlayer.prototype.feed = function (data) {
  if (!this.isTypedArray(data)) return
  data = this.getFormatedValue(data)
  var tmp = new Float32Array(this.samples.length + data.length)
  tmp.set(this.samples, 0)
  tmp.set(data, this.samples.length)
  this.samples = tmp
}

PCMPlayer.prototype.getFormatedValue = function (data) {
  var data = new this.typedArray(data.buffer),
    float32 = new Float32Array(data.length),
    i

  for (i = 0; i < data.length; i++) {
    float32[i] = data[i] / this.maxValue
  }
  return float32
}

PCMPlayer.prototype.volume = function (volume) {
  this.gainNode.gain.value = volume
}

PCMPlayer.prototype.destroy = function () {
  if (this.interval) {
    clearInterval(this.interval)
  }
  this.samples = null
  this.audioCtx.close()
  this.audioCtx = null
}

PCMPlayer.prototype.flush = function () {
  if (!this.samples.length) return
  var bufferSource = this.audioCtx.createBufferSource(),
    length = this.samples.length / this.option.channels,
    audioBuffer = this.audioCtx.createBuffer(this.option.channels, length, this.option.sampleRate),
    audioData,
    channel,
    offset,
    i,
    decrement

  for (channel = 0; channel < this.option.channels; channel++) {
    audioData = audioBuffer.getChannelData(channel)
    offset = channel
    decrement = 50
    for (i = 0; i < length; i++) {
      audioData[i] = this.samples[offset]
      /* fadein */
      if (i < 50) {
        audioData[i] = (audioData[i] * i) / 50
      }
      /* fadeout*/
      if (i >= (length - 51)) {
        audioData[i] = (audioData[i] * decrement--) / 50
      }
      offset += this.option.channels
    }
  }

  if (this.startTime < this.audioCtx.currentTime) {
    this.startTime = this.audioCtx.currentTime
  }
  bufferSource.buffer = audioBuffer
  bufferSource.connect(this.gainNode)
  bufferSource.start(this.startTime)
  this.startTime += audioBuffer.duration
  this.samples = new Float32Array()
}

export default PCMPlayer